Light Bomb was totally unlaunchable through the magic cannons because it would immediately produce a violent explosion even before being shot, or just after coming out. This couldn’t threaten the enemies in the slightest, and became instead a self-damaging weapon.
But during their tests, the Knight Temple’s researchers found out to their great surprise about a good benefit of the Light Bombs. That was their ability to superimpose their effects. After identical Light Bombs explode, the effects of the additional ones will add up, and the continuous increase of power could go up several-fold.
This discovery immediately brought great joy to them, and resurrected the researches on the Light Bombs that was close to being abandoned.